In vivo characterization of erythrocyte flow dynamics in human retinal capillaries

Abstract

Purpose : To estimate the velocity of erythrocytes in human retinal capillaries and to assess the velocity change with respect to time, using a high-speed adaptive optics near-confocal ophthalmoscope (AONCO).

Methods : The erythrocyte flow in retinal capillaries was imaged in human subjects with normal healthy retinae using an AONCO at a frame rate of 800 Hz over a field of view 1.2° X 0.3°. Cardiac pulse cycle was recorded simultaneously with retinal image acquisition. Spatiotemporal plots of erythrocyte movement were generated from the retinal videos and erythrocyte flow velocity measured from these plots using the Radon transform. Erythrocyte flux was counted in vessels containing single file cell flow. Characteristics of the flow dynamics were compared between 2 groups: 24-25 years old (n=4) and 50 years old (n=3).

Results : We imaged erythrocyte flow and measured the velocity in 93 parafoveal capillaries from 7 eyes of 7 subjects. Erythrocyte flow exhibited a pulsatile velocity waveform that was synchronized with the subject’s cardiac cycle. The waveform shape obtained in the old subjects, compared to that in the young subjects, showed distinctively less prominent change in velocity associated with the dicrotic notch (Fig. 1).

Conclusions : Due to high spatial resolution, high temporal resolution, and non-elicitation of visual response by infrared imaging, AONCO enables precise in vivo measurement of erythrocyte dynamics in human retinal capillaries. This capability may facilitate new investigations on the pathophysiology of the retinal microcirculation with applications for ocular and systemic diseases.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Fig.1. Erythrocyte dynamics in human retinal capillaries. A. Retinal capillaries imaged by the AONCO. Colored boxes indicate two capillary segments in which spatiotemporal plots B and C were generated. D. Erythrocyte velocity waveforms from these capillaries. Numbers indicate erythrocyte flux for each cardiac cycle. E. Electrocardiogram. F and G. Characteristics of flow dynamics and distinctive age-related velocity waveforms in young and old subject groups. Rr: rising rate; Tp: time of the velocity rising from valley to peak.